Electromagnetic water current meters are known to the art and typically include an electromagnetic coil mounted in a transducer body which may be of cylindrical form preferably with circular cross-section. Mounted at or near the surface of the transducer body are plural electrodes from which voltages are sensed by circuitry which processes the voltages and produces a signal related to water current velocity. It has been known for some time that under certain conditions it is desirable for the electrodes to project beyond the surface of the body of the transducer, i.e., to stick-out. See for example, my article in OCEANS '76 entitled "Electromagnetic Water Current Meter" presented at the Second Annual Conference of the Marine Technology Society and the Institute of Electrical and Electronics Engineers (September 15, 1976). See also "The Theory of Induced Voltage Electromagnetic Flow Meters", Bevir appearing in the Journal of Fluid Mechanics, Volume 43, part III, pages 577-590 (1970); "Measurements of Turbulent Fluctuation and Reynolds Stresses in a Tidal Current", Bowden et al, appearing in the Proceedings of the Royal Society (London) Series A, Volume 237 pages 422-38 (1956); "Electrodes for Magnetic Flow Meters", Gray, appearing in Water and Sewage Works (London), page R-93 (August 1972); "The Measurement of Sea Water Velocities by Electromagnetic Induction", Guelke et al, appearing in the Journal of the Institution of Electrical Engineers, Volume 94 part II, page 71 (1947); "The Theory of Electromagnetic Flow Measurement", Shercliff page 90 (Cambridge University Press, New York 1962); "A Two Component Electromagnetic Ship's Log", Tucker et al, appearing in the Journal of the Institute of Navigation, Volume 23, Page 302 (1970); "Electromagnetic Current Meters", Tucker, appearing in the Proceedings of the Society of Underwater Technology, (London) Page 53 (1972); and, "Electromagnetic Flow Metering", Webb, appearing in Institute of Technology, ISA March 1974.
Briefly stated, it is known that ideal flow going past a cylindrical electromagnetic water current meter can yield perfect cosine response. Ideal flow means that the fluid flow is described by potential theory, i.e., the flow has no vorticity. At the same time, it is also well known that real flow past a cylinder or sphere can be described in terms of two regions, the boundary layer region which is very thin next to the sensor or transducer wall and the potential flow region which exists everywhere except for this thin boundary region. Thus, by providing protruding electrodes, the sensitive area of the electrode extends beyond the transducer wall, and the boundary layer and into the region of potential flow for accurate measurement thereof. Inasmuch as the transducer is designed to sense fluid flow regardless of direction, and hence, has two pairs of electrodes, each pair spaced by 90.degree., if the fluid flow is directed directly at one of the diameters on which a pair of electrodes is located, that pair of electrodes will sense voltages proportional to the flow, and the other pair of electrodes will sense no flow at all. However, if the flow is not directed directly at a diameter on which a pair of electrodes exist, and this of course is typically the case, then a protruding electrode wil be in the wake of another electrode. The presence of the wake will disturb the velocity flow past the electrode which lies within it, resulting in less than ideal operation of the transducer.
It is therefore, one object of the present invention to provide electromagnetic water current meter having a transducer with stick-out electrodes while reducing the possibility that one of the electrodes will lie in the wake of another.